618 LYMPHATIC SYSTEM. 



they are not yet developed on the chyliferous vessels of the 

 mesentery. They are here seen, as in other classes, clus- 

 tered in reticulate plexuses around the great blood ves- 

 sels of the extremities and of the trunk. The lymphatics 

 from the lower extremities and the posterior parts of the 

 trunk, enter a large plexus or receptacle at the origin of the 

 coeliac artery, along with the lacteals from the lower portion 

 of the intestine. Those from the head and anterior parts of 

 the body enter the two great trunks of the thoracic ducts, to 

 pour their contents along with the chyle into the angle 

 between the subclavian arid jugular veins. As many as six 

 lymphatic glands have been detected on each side of the 

 neck, in some of the larger predaceous birds. Injected mat- 

 ters can still occasionally be forced to pass through the lym- 

 phatic vessels, from trunk to branches against the direction 

 of the valves, and Lauth sometimes found the injections ex- 

 travasated between the two coats of these vessels in birds. 

 In the goose, he observed the lymphatics extending along the 

 sides of the toes and over the interdigital membrane, form- 

 ing a plexus on the tarsus and lower part of the leg, collected 

 behind the knee into a single femoral trunk, which enters 

 through the crural arch into the pelvis ; here they form a 

 plexus, on each side, enveloping the renal veins, and send 

 their principal trunks into the renal or the sacral veins. The 

 chyliferous plexuses chiefly envelop the mesenteric, coeliac, 

 and aortic trunks, and, after receiving several lymphatics 

 from the abdominal and pelvic viscera and the posterior 

 parts of the trunk, they collect to form the commencement 

 of the thoracic ducts. The lymphatics from the lungs and 

 oesophagus, and from the wings, enter the thoracic ducts be- 

 fore their termination in the jugular veins, and the same 

 ducts receive also the lymphatic trunks from the sides of the 

 head and neck, excepting a branch from the right cervical 

 trunk which opens separately and directly into the right ju- 

 gular vein, and the left thoracic duct sometimes sends bran- 

 ches to open separately into the left subclavian. 



The fibrous and serous coats of the lymphatics, and their 

 general external cellular investment, are more distinct, espe- 

 cially in the larger trunks, in the mammalia, than in lower 

 classes ; their symmetrical pairs of opposed semilunar valves 

 are more numerous, more complete, and more effective in 



